A novel method for detecting an environmental pollutant, 4-nitrophenol (4-NP), by exploiting biomass-derived activated carbon (AC) is reported. The electrochemical performances of the 4-NP sensor were assessed by cyclic and linear sweep voltammetries. The presence of oxygen surface functional groups and heteroatoms (72.6% C, 6.1% H, 6.5% N, and 7.5% S) in the biomass-derived AC with high surface area (1555 m² g⁻¹) are found to be responsible for the excellent catalytic activities and reversible redox behaviors observed during the detection of 4-NP. The effects of pH of the electrolyte buffer solution, accumulated potential and duration as well as the analyte concentration on the electrocatalytic performance of the sensor were investigated. Consequently, a linear correlation between the cathodic reduction peak current with 4-NP concentration up to 500 μM with a detection limit and sensitivity of 0.16 μM and 5.810 μA μM⁻¹ cm⁻², respectively, were observed over the AC-modified GCE in 0.05 M acetate buffer solution (pH 5.0), surpassing the existing modified electrodes in the literature. The facile 4-NP sensor thus implemented is also advantageous for its simplicity, stability, reliability, durability, and low cost, rendering practical applications for real sample systems.